Histology Of The Respiratory Tract Flashcards
Respiratory epithelium
The respiratory system is largely lines by a type of epithelium called the respiratory epithelium
This lines the tubular/conducting portion of the respiratory system
Regarded as a pseudostratified columnar Cilliated epithelium
-Rests on a basement membrane
-Above the basement membrane lies a single layer of epithelial cells. However the nuclei of these cells are present at different heights giving the false impression that more than one layer of cells is present, but all of these cells are in contact with basement membrane
2 types of respiratory epithelium cells are present in respiratory epithelium
Most common are ciliated epithelial cells
Distributed amongst these ciliated epithelial cells is a population of mucus secreting goblet cells
Function of the nose
Filter, Humidify, Warm the inspired air
Also the site of olfaction- smelling
At the first part of nostrils (the bit where we can touch with our fingers)
This is lined by keratinising, stratified squamous epithelium
Further back, at the point where it becomes diffcult to touch
The mucosa changes to a non-keratinising stratified squamous epithelium
Nasal cavity
This is lined by respiratory epithelium
The connective tissue underneath the respiratory epithelium comprise of loose fibrous connective tissue, containing a number of seromucinous glands (glands that produce catarrh/snot) and a rich network of blood vessels
The nose- Olfaction
In the roof of the nasal cavity the epithelium is more specialised- olfactory epithelium
Olfactory epithelium is also a pseudostratified columnar ciliated epithelium but there is no goblet cells
The cillia are stereocillia- non motile
Contains basal epithelial cells but all cells are in contact with the basement membrane
Contains penetrating nerve fibres which all reach the surface of the epithelium
On the underlying connective tissue there is a rich network of serous glands of bowman. These secrete a watery fluid to help wash the surface clean
Large number of nerves in underlying connective tissue
Olfactory tissue lines only a small portion of the nose at the apex of the roof of the nose and extends a small distance into the septum and the lateral wall of the nasal cavity
Olfactory receptors cells- bipolar neurones
Dendrite extends to surface to become club-shaped ciliated olfactory vesicle
Need silver stains to highlight the nerves
The nasopharyngeal- further back into nose
Lined by respiratory epithelium
Function:
-Gas transport
-Humidification of inspired air
-Warming of inspired air
-Olfaction
Nasal sinuses
Air filled spaces within the bones of the skull and facial skeleton
Function:
-to lower the weight of the frontal skull
-to add resonance to the voice
-Humidify and warm inspired air
Lined by respiratory epithelium
The larynx
Cartilaginous box formed from almost entirely hyaline cartilage
Hyaline cartilage serve to hold the larynx open against negative pressure during inspiration
Site of voice production
Apart from the vocal cords, the inner aspect of the larynx is lined with respiratory epithelium
The vocal cords
Function- Voice production
Reinke’s space- Stratified squamous epithelium overlying loose irregular fibrous tissue
Almost no lymphatics
Contains vocal ligament (not shown in image) comprises dense fibroelastic connective tissue
Beneath this is the vocalis muscle
The trachea
Supported by hyaline cartilage arranged in a series of C shaped rings
Lined by respiratory epithelium
Function:
-Serves to conduct air to and from the lungs
Seromucinous glands in submucosa
C shaped cartilaginous rings are deficient posteriorly and the gap between the free ends of these rings is filled by a vertically orientated smooth muscle called trachealis
Trachealis muscle posteriorly
The bronchi and bronchioles
Trachea branches at the carina to form the main bronchi
Then within he lungs these branch again to dorm the lobar bronchi, then again to form the segmental bronchi, then again into a number of different bronchioles
All bronchi contain
smooth muscle, partial cartilaginous rings, respiratory epithelium, some basal neuroendocrine cells, seromucinous glands and goblet cells
Bronchioles have different histological appearance
-Do not contain partial cartilaginous rings, respiratory epithelium (this becomes simplified to ciliated columnar epithelium)
-Have smooth muscle, some basal neuroendocrine cells
- Contain few goblet cells. Most goblet cells replaced by Clara cells
Clara cells
Most numerous in terminal bronchioles- last part of the conducting airways
Roughly cuboidal
Pale staining cytoplasm, almost optically clear- vesicular cytoplasm
Mitochondria, smooth ER, secretory granules, no cilia;
Function (not completely certain):
-Secrete a lipoprotein that helps to prevent luminal collapse during exhalation- stops wall of bronchioles sticking together
-Role in oxidising inhaled toxins or in production of proteases to neutralise the effects of an inflammatory infection
-Role in removing surfactant in the lungs or are a stem cell population in lungs
Respiratory bronchioles.
First part of distal respiratory tract
Function:
-Gas exchange
-Gas transport
Link the terminal bronchioles and alveolar ducts
Lined with cuboidal ciliated epithelium
Walls of the respiratory bronchioles contain spirally arranged smooth muscle
With no cartilage
Alveoli
Site of gas exchange
150-400 million per lung
250 micrometer in diameter
Alveoli cell types- Type I pneumocytes
Squamous epithelial cells, they are flattened
40% of cell population- small number of cells cover large area
90% of surface area of the alveolus
Contain few organelles as they aim to be as thin as possible as they are important in providing part of the blood, air barrier
Alveoli cell types- Type II pneumocytes
60% of cell population
5-10% of surface area
Rounded cells
Round nucleus
Rich in mitochondria
Smooth and Rough ER
Produce surfactant- a protein which lowers surface tension in the lungs, making it easier to inflate the lungs
Alveoli cell types- Alveolar macrophages
Phagocytic cell derived from blood monocytes
They are found in interstitial connective tissue of the alveolar walls and also within the lumen of the alveoli
Phagocytose particulates including dusts and bacteria that have reached the alveolar air spaces and have not been trapped by the mucociliary escalator of those parts of the respiratory trac- so they appear pigmented in people who have a lot of carbon in airways
Enter lymphatics or leave via mucocilary escalator
Alveoli- blood-air barrier
Very thin
Comprises of type I pneumocystis lying on fused basement membrane of pneumoctyes and capillary that is shared with vascular endothelial cells
200-800nm thick
Exam question: how many layers are there in the blood-air barrier?
3- type I pneumocyte, basement membrane and vascular endothelial cells
4- surfactant layer, type I pneumocyte, basement membrane and vascular endothelial cells
Divide it into more- surfactant layer outer cell membrane of the type I pneumocyte, type I pneumocyte’s cytoplasm, type I pneumocyte’s cell membrane, basement membrane, cell membrane of the vascular endothelial cell, cytoplasm of vascular endothelial cell,
Alveoli- interstitium
This is where endothelial cells are not in direct contact with pneumocytes
Loose fibrous connective tissue comprising collagen and elastic fibres. Should be very little collagen and elastin in the walls of the alveoli
Contain fibroblasts, macrophages within walls of alveoli
Holes in walls of alveoli- Pores of Kohn
Help to equalise pressure between adjacent alveoli and help lungs inflate easily and evenly during inspiration
Allow infections to rapidly spread through lungs
The visceral pleura
2 layers: one adherent to the outer surface if the lungs and one adherent to the inner surface of the chest wall
Flat mesothelial cells rest on a loose fibrocollagenous connective tissue
loose fibrocollagenous connective tissue has an irregular inner layer that is formed of elastic tissue, a layer of fibrous connective tissue in the middle and an outer irregular layer of elastic tissue
